1. Field of the Invention
The present invention relates to a drive circuit system for a power window, for driving a motor to open and close the power window.
2. Description of the Prior Art
FIG. 7 shows a prior art drive circuit for a power window. A three-position control switch S operated by an occupant, an opening relay Ro adapted to be turned ON for opening the power window and a closing relay Rs adapted to be turned ON for closing the power window, are connected between a first line L.sub.1 connected to a power source 1 comprising a battery of 12 volts mounted on a vehicle and a second line L.sub.2 connected to a ground 2 of 0 volts. The control switch S includes a contact 3 biased toward a neutral position by a spring which is not shown. The contact 3 is capable of being connected to an opening terminal 4o or a closing terminal 4s by an occupant's operation. When the control switch S is operated from a neutral position as shown to an opening position to connect the contact 3 to the opening terminal 4o, a coil 5o of the opening relay Ro is excited, whereby a contact 6o is separated from an OFF terminal 7o and connected to an ON terminal 8o. As a result, a circuit of the power source 1 to the first line L.sub.1 to the ON terminal 8o of the opening relay Ro and the contact 6o to a third line L.sub.3 to a motor 9 to the third line L.sub.3 to a contact 6s of the closing relay Rs and an OFF terminal 7s to the second line L.sub.2 to ground 2, is formed, whereby the motor 9 is driven in an opening direction to open the power window.
When the control switch S is operated from the neutral position as shown to the closing position to connect the contact 3 to the closing terminal 4s, a coil 5s of the closing relay Rs is excited, whereby the contact 6s is separated from the OFF terminal 7s and connected to an ON terminal 8s. As a result, a circuit of the power source 1 K the first line L.sub.1 K the ON terminal 8s of the closing relay Rs and the contact 6s K the third line L.sub.3 K the motor 9 K the third line L.sub.3 K the contact 6o of the opening relay Ro and the OFF terminal 7o K the second line L.sub.2 K ground 2, is formed, whereby the motor 9 is driven in a closing direction to close the power window.
The opening relay Ro and the closing relay Rs are also capable of being controlled by an electronic circuit E. More specifically, when an opening transistor 9o of the electronic circuit E is turned ON, the coil 5o is connected to ground 2 without going through the control switch S, to close the opening relay Ro. When a closing transistor 9s of the electronic circuit E is turned ON, the coil 5s is connected to ground 2 without going through the control switch S, to close the closing relay Rs. Therefore, the power window can be opened and closed.
When the control switch S of the drive circuit system for the power window is wet with water due to the entering of water or the condensation of water, if leakage current Ao flows from the opening terminal 4o to the contact 3, the coil 5o is excited, thereby causing the power window to be opened. If leakage current As flows from the closing terminal 4s to the contact 3, the coil 5s is excited, thereby causing the power window to be closed. If the leakage currents Ao and As flow simultaneously, opposite ends of the motor 9 are brought into a higher potential, so that the motor 9 cannot be rotated, whereby it is impossible to open or close the power window. A problem also arises, when leakage currents Bo and Bs flow from the coils 5o, 5s to the ground 2. In addition, even if the electronic circuit E is subjected to a water-proofing treatment to prevent the mis-operation of the opening transistor 9o and the closing transistor 9s, a problem similar to that described above also arises, due to leakage current Co, Cs from a line extending from the electronic circuit E toward the control switch S to ground 2.